1. Field of the Invention
The present invention relates to transmission channel allocation methods and radio apparatuses using the same. More particularly, the present invention relates to a transmission channel allocation method and a radio apparatus using the same for allocating a channel to be used for transmission to a user requesting connection in a PDMA (Path Division Multiple Access) communication system where a plurality of users transmit and receive data such as audio and video using channels of the same frequency and the same time.
2. Description of the Background Art
In the field of the mobile communication systems such as portable telephones that have become extremely popular recently, various transmission channel allocation methods have been proposed to effectively use the frequencies. Some of the methods are actually in practice.
FIG. 13 is a diagram showing arrangements of channels in various communication systems of Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), and PDMA
Referring first to FIG. 13, the systems of FDMA, TDMA, and FDMA will be briefly described. FIG. 13(a) relates to the FDMA system, where analog signals of users 1-4 are frequency-divided to be transmitted in radio waves of different frequencies f1-f4. The signals of users 1-4 are separated by frequency filters.
In the TDMA system shown in FIG. 13(b), the digitized signals of respective-users are time-divided and transmitted in radio waves of different frequencies f1-f4 at every constant period of time (time slot). The signals of respective users are separated by frequency filters and by time synchronization between a base station and a mobile terminal device of each user.
Recently, the PDMA system has been proposed to improve the radio wave frequency usability to comply with the proliferation of portable telephones. In the PDMA system shown in FIG. 13(c), one time slot of the same frequency is spatially divided to transmit data of a plurality of users. In this system, signals of respective users are separated by frequency filters, time synchronization between a base station and a mobile terminal device of each user, and interference canceller such as adaptive arrays.
FIG. 14 is a schematic block diagram showing a transmission/reception system 2000 of a conventional base station for PDMA
Four antennas #1 to #4 are provided to distinguish between users PS 1 and PS 2.
In a reception operation, outputs of respective antennas are applied to RF circuit 101, where they are amplified by a reception amplifier and subjected to frequency conversion by local oscillation signals. Thereafter, any unwanted frequency signal is eliminated by a filter. Further, the signals are subjected to A/D conversion to be applied to a digital signal processor 102 as digital signals.
Digital signal processor 102 includes a channel allocation standard calculator 103, a channel allocation apparatus 104, and an adaptive array 100. Channel allocation standard calculator 103 preliminary calculates to determine if the signals from two users can be separated by the adaptive array. Based on the calculation result, channel allocation apparatus 104 provides to adaptive array 100 channel allocation information including user information for selection of the frequency and time. Adaptive array 100 separates the signal of a particular user by performing in real time a weighting operation on signals from four antennas #1 to #4 in accordance with the channel allocation information.
[Structure of Adaptive Array Antenna]
FIG. 15 is a block diagram showing a structure of a transmitting/receiving portion 100a corresponding to one user in adaptive array 100. Referring to FIG. 15, n input ports 20-1 to 20-n are arranged for extracting the signal of an intended user from input signals including a plurality of user signals.
The signals input to respective input ports 20-1 to 20-n are applied to a weight vector controlling portion 11 and multipliers 12-1 to 12-n through switch circuits 1xe2x80x941 to 10-n.
Weight vector controlling portion 11 calculates to obtain weight vectors Wli-Wni using the input signals, a training signal corresponding to a particular user signal which has preliminary been stored in a memory 14, and an output from an adder 13. Here, a subscript i indicates that the weight vector is used for transmission/reception with respect to the ith user.
Multipliers 12-1 to 12-n respectively multiply the input signals from input ports 20-1 to 20-n and weight vectors Wli-Wni for application to adder 13. Adder 13 adds output signals from multipliers 12-1 to 12-n for output as a reception signal SRX (t), which is also applied to weight vector controlling portion 11.
Further, transmitting receiving portion 100a includes multipliers 15-1 to 15-n receiving an output signal RTX (t) from the adaptive array of the radio base station and multiplying it by each of wli-wni that have been applied from weight vector controlling portion 11 for output. Outputs form multipliers 15-1 to 15-n are applied to switch circuits 10-1 to 10-n. In other words, switch circuits 10-1 to 10-n provide signals applied from input ports 20-1 to 20-n to a signal receiving portion 1R for signal reception, and provide signals from a signal transmitting portion IT to input/output ports 20-1 to 20-n for signal transmission.
[Operation Principle of Adaptive Array]
Now, the operation principle of transmitting/receiving portion 100a shown in FIG. 15 will be briefly described.
In the following, for simplification of the description, assume that four antenna elements are provided and two users PS are in connection at the same moment. Then, signals applied from respective antennas to receiving portion 1R are represented by the following equations.
xe2x80x83RX1(t)=h11Srx1(t) +h12Srx2(t)+n1(t)xe2x80x83xe2x80x83(1)
RX2(t)h21Srx1(t)-+h22Srx2(t)+n2(t)xe2x80x83xe2x80x83(2)
RX3(t)=h31Srx1(t)-+h32Srx2(t)+n3(t)xe2x80x83xe2x80x83(3)
RX4(t)h41Srx1(t) +h42Srx2(t)+n4(t)xe2x80x83xe2x80x83(4)
Here, a signal RXj (t) is a reception signal of the jth (j =1, 2, 3, 4) antenna, whereas signal Srxi (t) is transmitted from the ith (i =1, 2) user.
Further, a coefficient hji represents a complex coefficient of the signal from the ith user received by the jth antenna, whereas nj (t) represents a noise included in the jth reception signal.
The above equations (1) to (4) can be placed into vector formats as follows.
X(t)=H1Srx1(t)+H2Srx2(t)+N(t)xe2x80x83xe2x80x83(5)
X(t)=[RX1(t), RX2(t), . . . , RXn(t)]Txe2x80x83xe2x80x83(6)
Hi=[h1i,h2i, . . . , hni]T, (i=1,2) xe2x80x83xe2x80x83(7)
N(t)=[n1(t), n2(t), . . , nn(t)]Txe2x80x83xe2x80x83(8)
It is noted that [. . . ]T is the transposition of [. . . ] in the equations (6) to (8).
Here, X (t) is an input signal vector, Hi is a reception signal coefficient vector of the ith user, and N (t) is a noise vector.
With reference to FIG. 15, the adaptive array antenna outputs, as reception signal SRX (t), the signal obtained by multiplying input signals of respective antennas by weight coefficients W1i-Wni and adding them together. It is noted that there are four antennas in this example.
The operation of the adaptive array in the above described environment, for example when a signal Srxl (t) transmitted by the first user is extracted, is as follows.
An output signal y1 (t) from adaptive array 100 can be represented by the following equation that is obtained by multiplying input signal vector X (t) by weight vector W1.
yl(t)=X(t)W1Txe2x80x83xe2x80x83(9)
W1=[w11, w21, w31, w41]Txe2x80x83xe2x80x83(10)
In other words, weight vector W1 has weight coefficients wjl=1, 2, 3, 4) to be multiplied by jth input signal RXj(t).
By substituting input signal vector X (t) of equation (5) into equation (9), the following equation is obtained.
y1(t)=H1W1TSrx1(t)-+H2W1TSrx2(t)+N(t)W1Txe2x80x83xe2x80x83(11)
Here, if adaptive array 100 operates favorably, weight vector W1 is sequentially controlled by weight vector controlling portion 11 to satisfy the following simultaneous equation in accordance with a well-known method.
H1W1T=1xe2x80x83xe2x80x83(12)
H2W1T=0xe2x80x83xe2x80x83(13)
When weight vector W1 is perfectly controlled to satisfy the above equations (12) and (13), output signal y1 (t) from adaptive array 100 will eventually be represented by the following equation.
y1(t)=Srx1(t)+N1(t)xe2x80x83xe2x80x83(14)
N1(t)=n1(t)w11+n2(t)w21+n3(t)w31+n4(t)w41xe2x80x83xe2x80x83(15)
More specifically, signal Srxl (t) that has been transmitted by the first of the two users is obatained for output signal y1 (t).
On the other hand, referring to FIG. 15, input signals STX (t) to adaptive array 100 is applied to transmitting portion 1T of adaptive array 100 and applied to one inputs of multipliers 15-1 to 15-n. The other inputs of the multipliers are supplied with copies of weight vectors wli-Wni, which have been obtained by calculation in accordance with reception signals by weight vector controlling portion 11 as described above.
The input signals that have been weighted by the multipliers are transmitted to corresponding antennas #1 to #n through corresponding switches 10-1 to 10-n to be further transmitted Here, users PS1 and PS2 are distinguished as follows. Namely, radio signals from portable telephones are transmitted in frame configurations. The radio signal from the portable telephone mainly includes a preamble of a signal sequence known to the radio base station, and data (such as audio) of a signal sequence unknown to the radio base station.
The signal sequence of the preamble includes a signal column of information for determining if the user is desirable for the radio base station to communicate. Weight vector controlling portion 11 of adaptive array of radio base station 1 compares a training signal corresponding to user PS1 that is obtained from memory 14 and the received signal sequence for performing weight vector control (determination of weighting coefficient) to extract a signal which is likely to include the signal sequence corresponding to user PS1.
Recently, due to the rapid proliferation of portable telephones, the usability of channels is now approaching its limit. In the future, it is expected that allocation requests from users would exceed the number of available transmission channels. In such a case, the operation of the mobile communication system will be jeopardized unless some reasonable measures are taken.
In the above described PDMA system, one time-slot of the same frequency is spatially divided to transmit data of a plurality of users. Thus, a transmission channel must be allocated to each user such that interference among signals is eliminated by time synchronization between the base station and a mobile terminal device of each user. Then, it becomes difficult to maintain a sufficient communication quality unless allocation is performed to sufficiently reduce the interference among the plurality of users.
An object of the present invention is to provide a transmission channel allocation method capable of efficiently allocating a transmission channel to a user who is requesting connection (hereinafter referred to as a newly requesting user) while reducing interference between signals, and to a radio apparatus using the same.
In short, the present invention relates to a method of allocating to a plurality of terminal devices transmission channels for multiple connection to a base station having an array antenna in response to connection requests from the plurality of terminal devices. The method includes steps of: searching connectable transmission channel candidates among empty transmission channels based on a magnitude of cross correlation between a reception signal coefficient vector from a currently connected user and a reception signal coefficient vector of a user newly requesting connection; and allocating one of transmission channel candidates to the newly requesting user in accordance with the fact that a difference in reception signal electric power between the currently connected user and the newly requesting user does not exceed a prescribed value.
According to another aspect of the present invention, a radio apparatus for performing path-divided multiple connection with respect to a plurality of terminal devices is provided. The radio apparatus includes; array antennas; a plurality of reception signal separating portions; a reception signal power calculating portion; and a channel allocating portion.
The plurality of reception signal separating portions separate in real time reception signals by multiplying reception weight vectors of respective terminal devices by the reception signals from the adaptive array antennas.
The reception signal power calculating portion derives reception signal power of respective terminal devices.
The channel allocating portion determines a connectable transmission channel of empty transmission channels based on a cross correlation magnitude of reception signals from the already connected user and the newly requesting user as well as a difference in reception signal power, and allocates the transmission channel to the newly requesting user.
Therefore, a main advantage of the present invention is that a transmission channel allocation method is provided which enables path multiplex connection to be readily performed in terms of a base station, and enables allocation of the transmission channel to the newly requesting user whose reception power does not differ from that of the already connected user by a value exceeding a prescribed value, while maintaining a good communication quality.
Another advantage of the present invention is that a radio apparatus can be provided which enables path multiplex connection to be readily performed in terms of a base station, and enables allocation of the transmission channel to the newly requesting user whose reception power does not differ from that of the already connected user by a value exceeding a prescribed value, while maintaining a good communication quality.